From the particle production model (in the form of a set of inclusive distributions) and a few
other inputs (range-momentum relationship, inelastic interaction lengths, etc.) plus a geometry
subroutine (generally supplied by the user) CASIM computes star densities (i.e., nuclear interaction
densities) as a function of location and particle type throughout the target. From these star
densities, estimates of a number of quantities of radiobiological interest, e.g., dose equivalent due
to direct irradiation, CASIM also calculates momentum spectra of interacting particles, also as a
function of location in the shield and of particle type. The particles considered are: protons,
neutrons, and charged pions. A further option is the calculation of energy deposited by the
cascade. This quantity is a useful measure of target heating and can be related to light output of a
plastic scintillator embedded in the target (ionization calorimeters).

As presently designed, CASIM only yields the average energy deposited as a function of
location.

Alternative to the energy deposition option is an option which calculates a relative error of the
average (total) number of stars as a function of location.

CASIM contains a condensed version of SPUKJ (developed by J. Ranft at CERN, Geneva,
Switzerland) for the calculation of inclusive production cross sections of protons and pions due to
protons interacting with nuclei.

5. METHOD OF SOLUTION

CASIM is a Monte Carlo code system which studies the average development of internuclear
cascades when high energy particles are incident on large targets (shields) of arbitrary geometry
and composition. It is aimed at problems for incident particles in the range 20-1000 GeV/c and
does not study the transport of low energy particles (0.3 GeV/c). In contrast to similar code
systems, CASIM uses directly inclusive distributions, i.e., particle yields as a function of angle and
momentum (or other equivalent variables) from inelastic particle-nucleus interactions. The use of
weighting techniques avoids difficulties of random selection encountered in sampling complicated
distributions and allows the user to introduce bias in the sampling.

To save computing time, coding and storage all particles of an entire generation are represented
by two weighted Monte Carlo particles. One is chosen to propagate the cascade to the next
generation, the other to record the contribution of the present generation.

6. RESTRICTIONS OR LIMITATIONS

Momenta of particles included in the calculation should not be less than 0.1 GeV/C. A low
momentum cut-off above 0.3 GeV/c is recommended.

7. TYPICAL RUNNING TIME

1.5 minutes to prime the Monte Carlo plus about 1.0 minute per 5000 ``stars.'' Actual running
time depends strongly on the problem and on statistical accuracy desired. Typically this is in the
range of 20,000 to 200,000 stars.

8. COMPUTER HARDWARE REQUIREMENTS

CASIM was designed to run on an IBM 370/195 computer with approximately 400 K storage.